Avian leukosis virus (ALV) infections and expression are detrimental to the poultry industry (see e.g., Crittenden. (1991) Crit. Rev. Poult. Biol. 3:73-109. 1991; Goosen and de Boer (1983) Tijdschr. Diergeneeskd. 108:855-863; Payne (1998) Poult. Sci. 77:1204-1212; Zavala and Cheng (2006) Avian Dis. 50:209-215). There are five well-defined exogenous subgroups (A, B, C, D, and J) of ALV, which are associated with malignant neoplasms in chickens (see e.g., Crittenden. supra; Fadly et al. (2006) Avian Dis. 50:380-385; Fadly and Smith (1999) Avian Dis. 43:391-400; Fenton et al. (2005) Avian Pathol. 34:48-54; Lupiani et al. (2006) Avian Dis. 50:572-578; Meyers and Qualtiere (1977) J. Immunol. 118:1541-1548; Neiman et al. (1980) J. Virol. 34:178-186; Payne. supra; Payne et al. (1992) J. J. Gen. Virol. 73(11):2995-2997; Prukova et al. (2007) Avian Pathol. 36:15-27; Witter and Crittenden (1979) Int. J. Cancer 23:673-678; Zavala et al. (2006) Avian Dis. 50:201-208).
Numerous subgroup E endogenous viruses are present in the genome of most chickens (see e.g., Aggrey et al. (1998) Br. Poult. Sci. 39:39-41; Astrin. (1978) Proc. Natl. Acad. Sci. U.S.A 75:5941-5945; Astrin et al. (1980) Cold Spring Harb. Symp. Quant. Biol. 44(2):1105-1109; Bacon et al. (2004) Avian Pathol. 33:233-243; Bacon et al. (2000) Poult. Sci. 79:1082-1093; Benkel. (1998) Poult. Sci. 77:1027-1035; Boulliou et al. (1992) Poult. Sci. 71:38-46; Crittenden and Motta. (1975) Virology 67:327-334; Crittenden et al. (1974) Virology. 57:128-138; Gorbovitskaia et al. (1998) Poult. Sci. 77:605-614; Grunder et al. (1995) Poult. Sci. 74:1506-1514; Ignjatovic (1988) J. Gen. Virol. 69(3):641-649; Rovigatti and Astrin. (1983) Curr. Top. Microbiol. Immunol. 103:1-21; Tixier-Boichard et al. (1997) Poult. Sci. 76:733-742). The presence of endogenous virus in tissue culture cells can lead to contamination of vaccines (see e.g., Fadly et al. supra; Johnson and Heneine (2001) J. Virol. 75:3605-3612; Witter and Crittenden. supra) and to emergence of new recombinant viruses between exogenous and endogenous viruses (see e.g., Benson et al. The unique envelope gene of the subgroup J avian leukosis virus derives from ev/J proviruses, a novel family of avian endogenous viruses. J. Virol. 72:10157-10164. 1998; Smith et al. Novel endogenous retroviral sequences in the chicken genome closely related to HPRS-103 (subgroup J) avian leukosis virus. J. Gen. Virol. 80(Pt 1):261-268. 1999].
Cellular resistance/susceptibility to exogenous and endogenous ALV is specifically determined by autosomal tumor virus (TV) loci, namely TVA, TVB, TVC, and TVJ, which carry alleles either encoding receptors mediating a specific subgroup of viral entry or blocking an entry.
TVA encodes a membrane protein related to the family of low density lipoprotein receptors (see e.g., Bates et al. (1993) Cell 74:1043-1051; Elleder et al. (2004) J. Virol. 78:13489-13500; Young and He (1993) J. Virol. 67:1811-1816) and is mapped to chicken autosomal chromosome 28 (see e.g., Schmid et al. (2000) Cytogenet. Cell Genet. 90:169-218).
TVB is the most complex TV locus, and is related to the tumor necrosis factor (see e.g., Brojatsch et al. (1996) Cell 87:845-855). There are three TVB alleles, TVB*S1, TVB*S3, and TVB*R. TVB*S1 codes for susceptible receptors mediating infection by ALV subgroups B, D, and E and is dominant to both TVB*S3 and TVB*R; TVB*S3 codes susceptible receptors for infection by subgroups B and D and is dominant to TVB*R; TVB*R encodes a truncated receptor, which permits neither B, D, nor E subgroups of ALV infection (see e.g., Adkins et al. (2001) J. Virol. 75:3520-3526; Zhang et al. (2007) Avian Pathol. 36:283-291). TVB is cloned (see e.g Adkins et al. (2000) J. Virol. 74:3572-3578; Brojatsch et al. supra; Klucking et al. (2002) J. Virol. 76:7918-7921) and mapped to the chromosome 22 (see e.g., Smith and Cheng. (1998) Microb. Comp. Genomics 3:13-20).
TVC encodes a protein most closely related to immunoglobin family. TVC is cloned and mapped to chicken chromosome 28, close to the TVA locus (see e.g., Dren and Pani. (1977) J. Gen. Virol. 35:13-23; Elleder et al. (2005) J. Virol. 79:10408-10419).
TVJ is the latest identified locus and reported as the chicken Na+/H+ exchanger type 1 (chNHE1) gene. TVJ encodes a 90 kDa cell surface protein and is mapped to chromosome 23 (see e.g., Chai and Bates. (2006) Proc. Natl. Acad. Sci. U.S.A 103:5531-5536. 2006).
Avian leukosis viruses are retroviruses. Retroviruses have a tendency to integrate into the germ line and are transmitted vertically thereafter to subsequent generations as endogenous retroviral sequences (see e.g., Coffin et al. (1997) Retroviruses. Cold Spring Harbor Laboratory Press, New York; Crittenden. supra). There are reportedly more than 20 known subgroup E endogenous virus (ev) genes in the chicken, which encode for endogenous viruses or their components. Such genes are present in virtually all chicken genomes (see e.g., Rovigatti and Astrin. supra; Smith. (1986) Endogenous avian leukosis viruses. In: Avian leukosis. de Boer, ed. Martinus Nijhoff Publishing, Boston. pp. 101-120; Tereba and Astrin (1980). J. Virol. 35:888-894).
The nonessentiality of endogenous viruses for the chicken was first demonstrated by the identification of a fertile Leghorn rooster that lacked ev genes (see e.g., Astrin et al. (1979) Nature 282:339-341). This was supported by identification of similar chickens (see e.g., Chernov et al. (1984) Folia Biol. (Praha) 30:342-348), and at least two lines have been developed free of ev genes (Bacon. (2002) The National Registry of Genetically Unique Animal Populations: USDA-ADOL chicken genetic lines. Natl. Anim. Germplasm Program, East Lansing, Mich.; Crittenden. (1991) supra; Gavora et al. (1989) J. Anim. Breed. Genet. 106:217-224). However, White Leghorn chickens that are free of ev genes are extremely rare (see e.g., Gavora et al. supra), and with the exception of line 0, lines do not exist that have been characterized for susceptibility or resistance to specific subgroups of ALV.
Line 0 was the first developed chicken line characterized as free of subgroup E endogenous viruses, with resistance to subgroup E (C/E; TVB*S3/*S3), and is maintained specific pathogen free. Line 0 has been available to the research community since the 1980s (see e.g., Bacon. 2002. supra. Bacon et al. 2000. supra; Crittenden et al. (1984) Avian Dis. 28:1037-1056). Line 0 has been essential for detection of exogenous viruses in tissue samples from chickens and for eradicating exogenous ALV from breeder flocks following critical infections with ALV A in egg layers (see e.g., Crittenden et al. (1984) supra; Holmen et al. (1999) J. Virol. 73:10051-10060) and ALV J in broilers (Fadly and Smith. supra). Line 0 is also the source for a widely used immortalized cell line known as the UMNSAH-DF-1 cell line (see e.g., Maas et al. (2006) Biologicals. 34:177-181).
The UMNSAH-DF-1 cell line (also referred to as simply DF-1 and deposited under accession number ATCC CRL-12203) was the first line of spontaneously immortalized avian cells (Foster et al. U.S. Pat. No. 5,672,485). DF-1 was derived from the chicken embryo fibroblasts of line 0, and has been claimed as the world's only retroviral negative spontaneously immortalized avian cell line. Df-1 has been widely used in varied research and diagnostic tests since it became commercially available.
However, despite these and other advances, the need remains for improved spontaneously immortalized cell lines which are free of retroviruses, including ALV.
Fortunately, as will be clear from the following disclosure, the present invention provides for these and other needs.